3D rendering of the current and magnetic field lines of the loop in the emerging active region of Chen et al. (2014, 2015). The two panels show the side view (top panel) and the top view (bottom panel) on part of the computational box. The black lines are the field lines within the EUV loop (same as in Fig. 2) and the colored lines show current lines (or streamlines of the vector field of the current). The gray scale images show the vertical magnetic field at a height of z = 2.9 Mm at the base of the corona where the field already expanded and is rather smooth. The three color sets of current lines traced from different starting points: near the positive polarity (red), negative polarity (purple), and from the loop apex (green). We refer to Sect. 3.1.